Leonardo da Vinci’s linked system of gears for transferring motion was a gear train.
Leonardo made extensive studies of gear trains, which use two or more toothed wheels to transmit rotary motion from one shaft to another. By changing the sizes and numbers of teeth, a gear train can alter speed, torque, or direction.
His notebooks show interlocking gears in machines for lifting, winding, propulsion, and measurement. He carefully examined how the teeth should engage and how different gear ratios could produce useful mechanical effects.
Leonardo was not the first person to use gears; geared mechanisms had existed long before the Renaissance. His contribution was the detailed study and integration of gears into complex machine designs. A gear train is a mechanism, not one single finished invention, so surviving drawings represent a family of related studies.